Blowby gas includes gas leaking from a clearance between a cylinder and a piston to a crankcase of an engine. Fuel economy is improved by leading the blowby gas to an intake passage. Further, since a pressure inside the crankcase can be made to a negative pressure, a pumping loss of a piston can be decreased. An engine oil mist is included in the blowby gas and the oil is separated from the blowby gas by an oil separator. The blowby gas from which the oil is separated is caused to flow to the intake passage. The amount of the blowby gas flowing to the intake passage is regulated by a PCV valve.
For decreasing manufacturing costs, the oil separator is made from resin. Therefore, when the PCV valve is mounted to the oil separator, a heat from the engine is more difficult to be transmitted to the PCV valve via the oil separator than in a case where the oil separator is made from metal. As a result, when an ambient temperature is low, a water component contained in the blowby gas may freeze whereby a blowby gas passage in the PCV valve may be blocked by ice.
Japanese Patent Publication 2009-150351 discloses that a portion of the oil separator to which the PCV valve is mounted is made from metal having a high coefficient of thermal conductivity so that the heat from the engine is efficiently transmitted to the PCV valve.